1. Field of the Invention
The present invention is directed to a high efficiency impeller-type aerator for oxygenating the water supply of aquatic organisms, such as fish in a fish tank or bait in a live well.
2. Description of the Related Art
When fishing from a boat, it is a common practice to bring along bait fish in closed tanks known as live wells. Alternatively, larger boats may be equipped with a thru-hull bait well, wherein water from outside the boat is continuously pumped in, is passed through the tank, and is discharged over the side. In order to keep the bait fish alive for long periods of time, an aerator is provided to replenish the oxygen in the water as it is depleted by the bait fish. Several distinct types of aerators have been developed.
For example, U.S. Pat. No. 3,822,498 teaches an aerator for a live well wherein water is sucked through a pump and sprayed out a distributor manifold in the form of small jets above the surface of the water. As the jets pass through the air and then strike the surface of the water, the water picks up dissolved oxygen and entrained air bubbles. These systems are, however, disadvantageous for a number of reasons.
First, it is inevitable that jets of water will strike the fish and wash away the mucus outer coating which protects the fish. Second, energy consumption is high. Third, while the surface area of the live well may be aerated, the lower reaches of the bait well are not aerated, particularly when a large number of bait fish are kept in the bait well. Finally, aeration efficiency is relatively low, so that the total number of bait fish which can be kept in the well is correspondingly limited.
The aerator described in U.S. Pat. No. 5,582,777 (Vento et al), which utilizes a centrifugal pump, achieves a significantly improved level of oxygenation of the water in a live well while producing a gentle action which does not harm the bait fish. In fact, the unusually high level of oxygenation makes it possible to pack two to four times as many bait fish into a live well as had previously been possible.
The Vento et al use of the impeller cavity of a centrifugal or impeller type pump as an aerator mechanism represented a departure from conventional thinking, since it is the common experience of those in the industry that as air is introduced into the centrifugal pump it accumulates around the impeller, resulting in air-lock. That is, the accumulated air causes the impeller to spin freely, without pumping water. When water is not pumped through a live well, bait fish begin dying. Thus, conventional thinking was to take measures to prevent any air from getting into the centrifugal pump. Vento et al discovered that by regulating the amount of air introduced to the upstream (suction) side leading to a centrifugal pump, it becomes possible to induce a very thorough mincing of air and water in the pump impeller, resulting in emission of very fine mist of bubbles from the downstream (emission) side of the pump, without the problem of loss of suction. In other words, by supplying just the right proportions of air and water into the pump impeller, significant aeration can occur without the above-described problem of air lock.
Although the level of aeration is significantly improved with the Vento et al aerator as compared to conventional pumps using the same amperage, the inventor has noticed that there are two problems associated with this system. The first is that the Vento et al arrangement requires regulation of the input of air, either manually (via valve, clamp, etc.) or automatically (via optical turbidity sensors, etc.). The second is that the output from a centrifugal pump, once modified to introduce air according to the Vento patent, drops dramatically, for example, from 500 gallons per hour to 200 gallons per hour, thus the pump is operating at only 40% of its intended capacity.
In view of the foregoing, it is an object of the present invention to provide an improved centrifugal type aerator which does not require monitoring or regulating of the air input.
It is a further object of the present invention to provide an aerator which exhibits an improved capacity or flow rate.
It is a further object of the present invention to provide an aerator designed to avoid vapor lock of the centrifugal pump impeller.
It is yet a further object of the present invention to provide an aerator which achieves a high level of oxygenation.
The present inventor has investigated and experimented with various aerators and pumps, and produced what represents a significant improvement over the aerator invented previously by the present inventor, and which was described in U.S. Pat. No. 5,582,777 (Vento et al).
The present invention is built upon the Vento et al concept of introduction of air into the upstream (suction) side leading to a pump. The present inventor found he could use one of the following types of pumps: centrifugal, rotary, propeller and mixed flow. Each of these pumps can displace a liquid with a pump rotating element. The preferred pump is a centrifugal pump, such as a conventional rotary bilge pump, to cause churning and a very thorough mincing of air and water in the impeller cavity, followed by output of a mist of very fine bubbles from the downstream (emission) side discharged from the centrifugal pump. On closer examination of the Vento et al. device, the present inventor discovered and began investigating the problem of the significant inefficiency of the Vento et al. aerator.
After extensive and careful experimentation, the present inventor found that centrifugal pumps are designed to pump a non-compressible fluid, such as water. The energy imparted to the impeller blades is normally used to move the impeller blades against water to cause flow of water through the impeller cavity, developing a negative pressure or suction on the upstream side and a positive pressure or discharge head on the downstream side.
However, once air is introduced into the impeller cavity, the impeller energy is diverted to first expanding air in the negative pressure side of the impeller, and then re-compressing air on the downstream side of the impeller. Further, as the volume of air is increased (due to the negative pressure) on the inlet side, this expanded air displaces water, reducing the amount of water sucked into the impeller cavity. As the air exits the impeller cavity it is compressed to reduced volume, this constant compressing having the end effect of reducing the output at the downstream side of the impeller. Thus, the conventional centrifugal pump, when used to pump a fluid containing a compressible gas, works harder to pump less fluid.
Following further experimentation, the present inventor was able to determine that the above problems could surprisingly be solved by placing a first stage or booster impeller before the second stage or main impeller, with air being introduced at a point downstream of the first stage impeller outlet and upstream of the second stage impeller outlet.
Specifically, a preferred aerator of the present invention, designed for aeration of the water supply of aquatic organisms, can comprise: a centrifugal type pump comprising a first impeller having inlet and outlet edges, a second impeller having inlet and outlet edges, and a pump casing having at least one pump water inlet, one pump air inlet, and one pump water outlet, with the first and second impellers disposed between the pump water inlet and outlet, wherein the air inlet is positioned between the first impeller outlet edge and the second impeller outlet edge and is in communication with air, and wherein the water inlet and outlet are in communication with water.
Alternatively, the aerator may comprise first and second water pumps, each having a water inlet and a water outlet, with the water outlet of the first pump in fluid tight communication with the water inlet of the second pump, at least the second pump being a centrifugal pump including an impeller having inlet and outlet edges, the first pump being a smaller capacity pump than the second pump, and an air inlet positioned between the first pump outlet and the second pump impeller outlet edge and in communication with air.
Operationally, the device of the present invention has two stages: the boost stage and the main stage. The main stage is similar in construction to the Vento et al device, but it""s operation is modified by the pressure increase brought about in the boost stage. In the boost stage, water is drawn into the eye of the first impeller, or booster impeller, and is accelerated and thrown out, radially, at the impeller""s outlet edge. In the main stage, air from the air inlet and pressurized water from the booster impeller are co-mingled or minced by the main impeller. Due to the increase in water pressure brought about by the booster impeller, the main impeller does not have to draw as hard on water, i.e., does not have to create a significant negative pressure gradient prior to the main impeller inlet. Since the negative pressure gradient is reduced, the air bubbles being introduced do not expand to the degree experienced in the original Vento et al device. Thus, the main impeller is not expending energy on expanding air. Further, since the air being introduced into the main stage is more compressed and less expanded, the air displaces less water, and the pumping capacity of the main impeller is significantly improved. Finally, since air is not being introduced to the booster impeller, and since the booster impeller is continuously providing water to the main impeller, i.e., is continuously priming the main impeller, it becomes impossible to xe2x80x9cvapor lockxe2x80x9d the main impeller. Thus, there is no need to monitor or control the aerator of the present invention to prevent vapor lock.
The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood and so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other aerators for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent structures do not depart from the spirit and scope of the invention as set forth in the appended claims.